Vibrio parahaemolyticus(VP) is a pathogen of bacterial food poisoning associated with shellfish.VP,which is detected both in human and fish,has even higher concentrations in oysters and other filter-feeding shellfish.In order to study the relationship of VP densities versus water quality factor including water salinity,temperature,pH and dissolved oxygen in the course of oyster culture,we detected total VP densities in the oyster and water quality factor at the oyster farm in Yangxi,Guangdong from March to November in 2009.The results showed that the detection ratio of total VP in oysters was 94.38%.The water temperature was correlated positively with total VP in oysters,but the salinity was correlated negatively with total VP in oysters.The dissolved oxygen and pH didn’t show correlation with total VP in oysters.Based on the regression analysis,a quadratic relationship for VP densities versus water temperature and salinity was found.The regression equation of VP densities versus water temperature was:LgVP=0.093T-0.685(R²=0.336);The regression equation of VP densities versus salinity was:LgVP=1.199+0.116S-0.004S²(R²=0.217);The best fit regression equation of VP densities versus water temperature and salinity was LgVP=-1.941+0.116T+0.058S-0.001S²>(R²=0.414).The results of this paper may provide some reference data for the risk analysis of VP during oyster culture.